Structural deformation of the rocks of the western Sierra Nevada has developed zones of faulting and of minor partings that are only slightly dilatant, appropriate in deep-seated environment. Gold-quartz veins and dikes of igneous rocks contain inclusion breccias and occupy partings of highly dilatant character--features that may result from the inflation of deep-seated rocks by an injected fluid but would only be associated with near-surface fault fissures. The folding of inter-vein and inter-dike wall rock during inflation of the partings is discordant with an open-fissure environment. Most of the structures found in the gold-quartz veins are likewise found in igneous dikes of comparable size--parallel mechanisms of emplacement are indicated.

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